Practically all road signs are normally provided with a so-called retroreflective material (thin adhesive tape). Such materials increase the visibility and detectability of the road signs, provided that light from the car headlights actually impinges upon the sign. In the countryside, this is almost always the case. In cities, however, it is common that the light beams from the car headlights do not reach the road signs, since a great many road signs are placed on overhead frame structures bridging the roadway, or so high up that they are outside the light/darkness border of dipped headlights. Since signs in cities have to be well lit up, separate light fittings are often mounted on or above the road signs.
U.S. Pat. No. 2,017,617 discloses how to direct light from ordinary street lights to a sign, in this case a street sign, by means of an adjustable flat mirror. The sign is of conventional construction and has no special reflecting power.
U.S. Pat. No. 1,858,975 discloses an advertising sign which is made of a transparent material and, at its back, has reflecting surfaces so directed that they reflect light at an angle which, to people within a given area in front of the sign, makes the advertising sign look as if lit up. Planar as well as curved mirrors are disclosed.
SE-B-65,708, U.S. Pat. Nos. 2,310,790, 1,298,840 and DE-A-2,301,868 disclose reflectors of a type reflecting light approximately in the direction of the light source. The rear surface of the reflector is prismatically designed, and has angularly disposed reflecting surfaces which, in some cases, are completely planar and, in other cases, are conical or spherical.
SE-B-438,215 and corresponding U.S. Pat. No. 4,252,409 disclose a reflector for game, which is in the form of a transparent plate in which the surface opposite to the light-admitting surface is made up of toroidal surfaces which are juxtaposed and support a reflecting layer. The optical axes of the toroidal surfaces are arranged at an angle to the normal of the light-admitting surface. When mounted, the reflectors are positioned at such an angle to the verge of the road, and thus to the beams from vehicle headlights, that the beams are reflected to the surroundings, thereby scaring off the animals.
U.S. Pat. No. 2,132,649 discloses a display sign having a curved reflecting surface behind opaque letters or characters so that these are illuminated from the back, giving the impression of a background surface illuminated from behind.
U.S. Pat. No. 1,782,721 discloses an advertising sign having internal reflecting surfaces for deflecting light arriving obliquely from above, in such a manner that the light will be construed as an internal source of illumination in the advertising sign.
In spite of the existing prior art, there is, however, a need for a reflecting material and reflecting signs, especially road signs, of a reflecting power which enables efficient use of the street light in order to make visible the information at issue.
One object of the invention is, therefore, to provide a reflecting material of suitable reflecting power. Another object is to provide a suitable reflecting material for display signs, especially road signs, which when mounted reflects light from ordinary street lights in such a direction that an observer of the sign perceives it in a manner similar to the reflections from a retroreflecting material illuminated by car headlights, but being stronger than such reflections. At the sign, the strength of the light from street lamps is much greater, often up to 100 times, than that of the light from car headlights impinging upon the sign.